Ignition circuit



April 25, 1967 H. P. QUINN IGNITION CIRCUIT Filed June 22. 1964 INVENTOR /%44 55 R 00w BY 7774a p 051.4;

ATTORNEYS United States Patent 3,316,449 IGNITION CIRCUIT Halsey P. Quinn, Morris Plains, N.J., assignor to Tnng-Sol Electric Inc., a corporation of Delaware Filed June 22, 1964, Ser. No. 376,725 6 Claims. (Cl. 315--214) This invention relates to an ignition circuit for internal combustion engines which produces a high voltage spark for each spark plug. It has particular reference to a means for producing a high voltage pulse which does not depend upon the speed of the engine. The circuit uses silicon controlled rectifiers, one of which is constructed so that it may be turned off as well as on.

Many types of ignition circuits have been developed for supplying spark plugs with high voltage discharges which ignite the charge within a piston chamber. Substantially all of these circuits or arrangements require a definite engine speed before operating properly. While this characteristic does not generally affect the operation during normal speed operations, there are conditions at slow speed when starting, and at very high speeds, wherein the circuit does not produce sufiicient voltage or wherein the Voltages in the circuit are more than normal and may cause insulator breakdown. The present circuit can be arranged to provide an 80 microsecond, high voltage spark which is quite independent of the speed of the engine. The usual breaker contacts are employed but they pass very little current and for this reason have a long life.

As used throughout the specification and claims, the term silicon controlled rectifier refers to a semiconductor having four layers and three terminals. This component has been described in prior publications and is wellknown in the art. The term gate controlled switch (G.C.S.) is the same as the silicon controlled rectifier except that it is arranged to turn off the current flow as well as turn it on. For this purpose a positive pulse is applied to the control electrode to make the device conductive and a negative pulse is applied to the control electrode to make the device nonconductive.

One of the objects of this invention is to provide an improved ignition circuit which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to provide a high voltage spark of constant duration which is independent of the speed of the engine.

Another object of the invention is to increase the current flow through semiconductor components by using only silicon rectifier devices.

Another object of the invention is to reduce the current carried by the breaker contacts.

The invention comprises an ignition circuit for internal combustion engines having a spark plug in each combustion chamber and includes, a source of direct current and a pair of breaker contacts controlled to open and close in synchronism with the movements of the engines pistons. The circuit also includes a first charging circuit comprising an inductor and the anode-cathode circuit of a first silicon controlled rectifier. The breaker contacts are bridged across the anode-cathode circuit of this first rectifier. A second charging circuit comprises a primary winding of a charging transformer, a gate controlled switch and a voltage divider. A storage circuit is provided for collecting and storing a charge in a storage capacitor prior to discharging the capacitor through the primary winding of an output transformer. This charging circuit includes the storage capacitor, the secondary winding of the charging transformer, and a silicon rectifier. The storage capacitor is discharged through the anodecathode circuit of a second silicon controlled rectifier. The high voltage pulse is applied to the spark plugs by the usual distributor and the secondary winding of the output transformer.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings:

FIG. 1 is a schematic diagram of connections of the preferred embodiment of the ignition circuit.

FIG. 2 is a schematic diagram of an alternate circuit showing only a portion of the complete arrangement.

FIG. 3 is a graph indicating some of the voltages and currents which exist in the circuit during its operation.

Referring now to FIG. 1, the circuit comprises the usual battery 10, an on-ofi" switch 11, and a pair of breaker contacts 12 which are operated by a cam 13 secured to a shaft 14 which connects with a rotary arm 15 in the distributor 16. The distributor 16 contains the usual stationary contacts 17, each connected to one of a plurality of spark plugs 18.

The circuit also includes an inductor 20 having a wind ing on a ferromagnetic core 21. The inductor is connected in series with a rectifier 22, a limiting resistor 23, and a first silicon controlled rectifier 24. The breaker contacts are connected across the anode-cathode circuit of this first control rectifier.

The circuit also includes a charging transformer 25 having a primary winding 26, a secondary Winding 27, and a core 28. The primary winding 26 is connected in series with the anode and cathode of a gate controlled switch 30 and a voltage divider 31 having a mid-point adjustable connector 32. A capacitor 33 is shunted around the gate control switch 30 in order to slow down the rate of rise of voltage during the turn-off operation of this component in order to reduce the generation of heat within the switch.

The circuit contains a storage capacitor 34, this capacitor receiving its charge from a charging circuit which includes the secondary winding 27 of charging transformer 25, a diode rectifier 35, and the primary winding 36 of an output transformer 37 having a secondary winding 38 coupled to the distributor 16. Storage capacitor 34 is discharged through the primary winding of output transformer 37 by means of a second silicon controlled rectifier 40 having its anode-cathode circuit connected between one terminal of the storage capacitor and the negative terminal of the battery 10'.

Three coupling circuits are employed to control the two silicon controlled rectifiers and the gate controlled switch. One of these circuits comprises a resistor 41 connected between the mid-point 32 of voltage divider 31 and the control electrode of the silicon controlled rectifier 24. A second coupling circuit comprises a capacitor 42 connected between one terminal of resistor 23 and the control electrode of the second silicon controller rectifier 40. This circuit also includes a diode rectifier 43 which is connected between the control electrode of rectifier 4t} and the ground conductor 44 in order to bypass the reverse pulse when the gate controlled switch 30 is being turned off. A third coupling circuit comprises a capacitor 45 connected between the same terminal of resistor 23 and the control electrode of gate controlled switch 30.

The operation of this circuit is as follows: When points 12 are open before starting, no current flows in any portion of the circuit because both silicon controlled: rectifiers 25 and 40 are in their nonconductive condition and the gate controlled switch 30 is also nonconducting. When points 12 are closed for the first time, current flows through inductor 20, diode 22, resistor 23, and points 12 to conductor 44 to set up a current which provides magnetic flux in core 21. The variations of current value-in this and other circuits may be understood by ref- 7 pulse through capacitor 45.

34 has not been charged The pulse transmitted through capacitor 45 turns on the gate controlled switch 30 and a current flows from battery 10 through primary winding 26, gate controlled switch 30, andthe voltage divider '31. This current produces a magnetic flux in core 28.

This current builds up slowly because of the inductance in winding 26 but when it reaches a sufficient value the voltage at contact point 32 is sufficient to apply a voltage to the control electrode of rectifier 24 to make it conducting whereby current is restored to the inductor winding (time T2). Rectifier 24 remains in its conducting condition until breaker points 12 are again closed (at time T3). The points short-circuit the rectifier and cause it to revert to its nonconducting condition;

When the silicon controlled rectifier 24 was turned on, capacitor 45 was discharged and a pulse through it was applied to the gate controlled switch to turn it off. This action reduces the current through winding 26 to zero and the flux in core 28 collapses, thereby generating a current pulse (56, see FIG. 3) in winding 27 which applies a quantity of electricity to the storage capacitor 34 through diode 35 charging it to about 300 volts. Next, the points open for a second time and current pulses are again sent through capacitors 42 and 45 as before. This time the silicon controlled rectifier is made conductive and the storage capacitor 34 discharges through this rectifier and primary winding 36 of the output transformer 37, thereby sending a high voltage pulse through distributor 16, to one of the spark plugs 18.

The action continues sending a pulse from inductor 20 to control the current through primary winding 26 and when this current is turned off, another pulse is applied to the storage capacitor which then discharges to send a pulse through the output transformer to one of the plugs. It should be obvious from the above explanation that the time delay between the closing of the contact points 12 and the activation of the first controlled rectifier 24 depends only upon the rate of charge through inductor 20. Also, the control of the other components in this circuit does not depend upon the speed of the engine.

The circuit shown in FIG. 2 contains the same battery 10, the same switch 11, and the same coupling capacitors 42 and 45. Also the breaker points 12 and the operating cam 13 are the same as shown in FIG. 1. In FIG.-2 the inductor has been replaced by a transformer 51 having a primary winding 52,a core 53, and a secondary winding, 54. Both windings are connected to the junction of capacitors 42 and in series with rectifiers 22A and 22B respectively. The grid controlled rectifier 24 and the resistor 23 are the same as before. This circuit is more reliable and permits the use of larger inductances :and therefore more powerful transfer pulses. In the circuit shown in FIG. 1, the inductanceof primary wind- Sing 26 may be too high, causing the current to build up slowly when the 6.0.8. 30 is triggered by a positive If the anode-cathode current is less than a critical value, the 6.0.8. is not made conductive and no transfer pulse to charge capacitor 34 is generated. The circuit shown in FIG. 2 eliminates this problem by providing more inductance (in winding 54) to charge'ca-pacitor 45, therefore lengthening the time of the trigger pulse. By using a transformer rather than a single coil, it is possible to have a high inductance secondary for a long trigger pulse, and a low inductance primary for a fast Charging time,

this chart that the firing pulse occurs when the points open at time Tl. This pulse is created by the discharge pulse 55 through the silicon controlled rectifier 40. It is also obvious from the curve shown in FIG. 3

that the charging rate, illustrated by curve 56 for charging storage capacitor 34, starts adefinite time after the opening of the points 12 regardless of the speed of the engine.

The foregoing disclosure and drawings disclose two embodiments of the present invention. It will be obvious to those skilled in the prior art that many changes can be made in these embodiments without departing from the'spirit and scope of the invention. Therefore, it will be understood that this is intended to cover all changes in the disclosed embodiments which do not depart from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. An ignition circuit for an internal combustion engine having a spark plug in each combustion chamber comprising,

a source of direct current;

a pair of breaker contacts controlled to open and close in synchr-onism with the movements of the engines pistons;

an inductor including a winding on a ferromagnetic core for generating a current pulse when current through the winding is cut off;

a charging transformer including a primary winding and a secondary winding on a ferromagnetic core for generating a charging pulse in its secondary winding when current is cut off in its primary winding;

a storage capacitor for storing a quantity of electricity produced 'by said secondary winding;

an output transformer including a primary winding and a secondary winding for transferring the electricity stored in the storage capacitor to a distributor and spark plugs;

a first charging circuit connected across said source of current including in series, said inductor, and a first silicon controlled rectifier having an anode, a cathode, and a control electrode, said breaker contacts connected across the anode and cathode;

a second charging circuit connected across said source and including in series, the primary winding of the charging transformer, a voltage divider, and a gate controlled switch having an anode, a cathode, and

a control electrode;

a first coupling circuit comprising a resistor connected between a mid-point on the voltage divider and the control electrode of the first silicon controlled rectifier for making the rectifier conductive when a current through the primary winding of the charging transformer reaches a predetermined value;

a capacitor charging circuit connected across the secondary winding of the charging transformer including in series, said storage capacitor, and the primary winding of the output transformer;

a storage capacitor discharge circuit for discharging the storage capacitor and generatnig a spark at one of the spark plugs, said discharge circuit including in series connection, the storage capacitor, the primary winding of the output transformenand the anode-cathode circuit of a second silicon controlled rectifier;

a second coupling circuit comprising a first capacitor connected between one end of the inductor and the control electrode of said silicon controlled rectifier for making the second rectifier conducting when the breaker contacts are opened;

and a third coupling circuit comprising a second capacitor connected between one end of the inductor and the control electrode of the gate controlled switch for making the switch conductive when the breaker contacts are opened and for making the switch nonconductive when the current through the inductor is cut off.

2. An ignition circuit as claimed in claim 1 wherein a diode rectifier is connected in series with said first charging circuit to prevent the discharge of two coupling capacitors connected between the first charging circuit and other controlled rectifiers.

3. An ignition circuit as claimed in claim 1 wherein said capacitor charging circuit includes a diode rectifier in series with the secondary Winding to prevent the discharge of the storage capacitor through the secondary winding.

4. An ignition circuit as claimed in claim 1 wherein a capacitor is connected across the anode-cathode circuit of the gate controlled switch to prevent the rapid rise of voltage across these components when current through the switches is cut off.

5. An ignition circuit as claimed in claim 1 wherein said inductor is replaced by a transformer having a primary winding connected in series between the positive terminal of the source of potential and the anode of the first silicon controlled rectifier, and a secondary Winding connected in series between the primary winding of the charging transformer and the junction of said first and second coupling capacitors.

6. An ignition circuit as claimed in claim 1 wherein a diode rectifier is connected across the control electrode and the cathode of the second silicon controlled rectifier to by-pass the negative pulse generated by the reduction of current in the inductor when the gate controlled switch is being made non-conductive.

References Cited by the Examiner UNITED STATES PATENTS 3,032,685 5/1962 Loomis 3l5209 3,049,642 8/1962 Quinn 3 l5309 3,131,327 4/1964 Quinn 3l5209 JOHN W. HUCKERT, Primary Examiner. D. O. KRAFT, Assistant Examiner. 

1. AN IGNITION CIRCUIT FOR AN INTERNAL COMBUSTION ENGINE HAVING A SPARK PLUG IN EACH COMBUSTION CHAMBER COMPRISING, A SOURCE OF DIRECT CURRENT; A PAIR OF BREAKER CONTACTS CONTROLLED TO OPEN AND CLOSE IN SYNCHRONISM WITH THE MOVEMENTS OF THE ENGINE''S PISTONS; AN INDUCTOR INCLUDING A WINDING ON A FERROMAGNETIC CORE FOR GENERATING A CURRENT PULSE WHEN CURRENT THROUGH THE WINDING IS CUT OFF; A CHARGING TRANSFORMER INCLUDING A PRIMARY WINDING AND A SECONDARY WINDING ON A FERROMAGNETIC CORE FOR GENERATING A CHARGING PULSE IN ITS SECONDARY WINDING WHEN CURRENT IS CUT OFF IN ITS PRIMARY WINDING; A STORAGE CAPACITOR FOR STORING A QUANTITY OF ELECTRICITY PRODUCED BY SAID SECONDARY WINDING; AN OUTPUT TRANSFORMER INCLUDING A PRIMARY WINDING AND A SECONDARY WINDING FOR TRANSFERING THE ELECTRICITY STORED IN THE STORAGE CAPACITOR TO A DISTRIBUTOR AND SPARK PLUGS; A FIRST CHARGING CIRCUIT CONNECTED ACROSS SAID SOURCE OF CURRENT INCLUDING IN SERIES, SAID INDUCTOR, AND A FIRST SILICON CONTROLLED RECTIFIER HAVING AN ANODE, A CATHODE, AND A CONTROL ELECTRODE, SAID BREAKER CONTACTS CONNECTED AVROSS THE ANODE AND CATHODE; A SECOND CHARGING CIRCUIT CONNECTED ACROSS SAID SOURCE AND INCLUDING IN SERIES, THE PRIMARY WINDING OF THE CHARGING TRANSFORMER, A VOLTAGE DIVIDER, AND A GATE CONTROLLED SWITCH HAVING AN ANODE, A CATHODE, AND A CONTROL ELECTRODE; A FIRST COUPLING CIRCUIT COMPRISING A RESISTOR CONNECTED BETWEEN A MID-POINT ON THE VOLTAGE DIVIDER AND THE CONTROL ELECTRODE OF THE FIRST SILICON CONTROLLED RECTIFIER FOR MAKING THE RECTIFIER CONDUCTIVE WHEN A CURRENT THROUGH THE PRIMARY WINDING OF THE CHARGING TRANSFORMER REACHES A PREDETERMINED VALUE; A CAPACITOR CHARGING CIRCUIT CONNECTED ACROSS THE SECONDARY WINDING OF THE CHARGING TRANSFORMER INCLUDING IN SERIES, SAID STORAGE CAPACITOR, AND THE PRIMARY WINDING OF THE OUTPUT TRANSFORMER; A STORAGE CAPACITOR DISCHARGE CIRCUIT FOR DISCHARGING THE STORAGE CAPACITOR AND GENERATING A SPARK AT ONE OF THE SPARK PLUGS, SAID DISCHARGE CIRCUIT INCLUDING IN SERIED CONNECTION, THE STORAGE CAPACITOR, THE PRIMARY WINDING OF THE OUTPUT TRANSFORMER, AND THE ANODE-CATHODE CIRCUIT OF A SECOND SILICON CONTROLLED RECTIFIER; A SECOND COUPLING CIRCUIT COMPRISING A FIRST CAPACITOR CONNECTED BETWEEN ONE END OF THE INDUCTOR AND THE CONTROL ELECTRODE OF SAID SILICON CONTROLLED RECTIFIER FOR MAKING THE SECOND RECTIFIER CONDUCTING WHEN THE BREAKER CONTACTS ARE OPENED; AND A THIRD COUPLING CIRCUIT COMPRISING A SECOND CAPACITOR CONNECTED BETWEEN ONE END OF THE INDUCTOR AND THE CONTROL ELECTRODE OF THE GATE CONTROLLED SWITCH FOR MAKING THE SWITCH CONDUCTIVE WHEN THE BREAKER CONTACTS ARE OPENED AND FOR MAKING THE SWITCH NONCONDUCTIVE WHEN THE CURRENT THROUGH THE INDUCTOR IS CUT OFF. 